An advanced method for detecting infrared light has recently been developed which utilizes mercury cadmium telluride (HgCdTe). A zinc sulfide (ZnS) layer is generally deposited onto the HgCdTe layer to act as an insulator for the detector. Dry etching techniques for etching through the HgCdTe and ZnS layers have used energy from a remote microwave plasma discharge for activating an etchant to reactively remove selected portions of the HgCdTe and ZnS layers of a wafer.
Despite advancements in this dry etching technique, special arrangements must be taken to excite a fluorine-containing gas in a microwave discharge remote from the reaction zone of the wafer. Additionally, precautions must be taken in handling the fluorine gas because of its corrosive nature. Other problems have resulted from using a hydrocarbon gas as the etchant, as under some conditions of flow rates and pressures the hydrocarbon gas will polymerize to form undesirable films on the surfaces of the wafer.
When forming vias in the wafer, prior dry etchants tend to damage other areas which are not intended to be contacted. This type of unintentional damage can result in electrical short circuiting of the integrated circuit. Additionally, dry etching techniques tend to leave rough surfaces when forming vias in a wafer due to non-uniform etching of the separate components in a multi-component system, such as HgCdTe. Such roughness can cause operational problems related to the damage produced in the material.
Therefore, a need has arisen for a process for dry etching infrared detector layers which does not require a remote microwave plasma source for exciting a fluorine gas. It would also be desirable to have a dry etching process available which can eliminate the polymerization of films on the surface of the wafer. Additionally, a need has arisen for a method of forming a via which does not damage the wafer surface by inadvertent etching in protected (resist-pattern-defined) areas and which forms smooth via walls.